Automatic exposure control system for a single lens reflex camera

ABSTRACT

An automatic exposure control system for a single lens reflex camera, in which provision is made such that after the operations of focusing and the like have been carried out with the diaphragm opened at its maximum aperture, the shutter button is depressed so that the diaphragm may be closed to a predetermined aperture stop value simultaneously with the jump up of the reflector mirror and the amount of light passed through the lens may be measured by means of a photo-conductive element located behind the mirror to achieve the time control for the shutter speed.

United StatesPatent I Uchida et a1.

[54] AUTOMATIC EXPOSURE CONTROL SYSTEM FOR A SINGLELENS REFLEX CAMERA a[72] Inventors: Yasuo Uchlda; Yoshltaka Kuroyanagi, both of Tokyo, Japan[73] Assignee: Kanlshiroku Photo Industry Co.,

Ltd

[22] Filed: Dec. 4, 1970 [21] Appl. -No.: 95,233

[30] Foreign Application Priority Data Dec. 11, 1969 Japan.......44/99028 [52] US. Cl. ..95/10 PO, 95/10 CT, 95/64 B [51] Int. Cl...G03b 7/08 [58] Field of Search ..95/l0 C, 10 CT, 10 PO 51 Sept.19,1972

[56] l A References Cited UNITED STATES PATENTS Erickson ..95/ IO CTPrimary Examiner-Samuel S. Matthews Assistant Examiner-Russell E. Adams,Jr.

' Attorney-Harry C. Bierman, Jordan B. Bierman and Bierman & Bierman [57] ABSTRACT An automatic exposure control system for a single lensreflex camera, in which provision is made such that after the operationsof focusing and the like have been carried out with the diaphragm openedat its maximum aperture, the shutter button is depressed so that thediaphragm may be closed to a predetermined aperture stop valuesimultaneously with the jump up of the reflector mirror and the amountof light passed through the lens may be measured by means of aphoto-conductive element located behind the mirror to achieve the timecontrol for the shutter speed.

9 Claims, 4 Drawing Figures PATENTEDSEP 19 I972 3.691. 917

sum 1 BF 3 Fig.1

Reducfion of aperture stop Depression of reL age butt Restored Lon "YPkP f; ReLease 0T first ReLeasc of second W bLLnd of shutter bLLndofshutter mLrror t l. l

Photomet y Actuation Of Tim mg device Fig.3

O 8 Time YAsw mmon INVENTORS Yul-nun: lfwtoyfi ll AUTOMATIC EXPOSURECONTROL SYSTEM FOR A SINGLE LENS REFLEX CAMERA The present inventionrelates to an automatic exposure control system for a single lens reflexcamera which carries out the automatic exposure control by measuring theamount of light passed through an object, and more particularly to anautomatic exposure control system for a single lens reflex camera whichautomatically controls the exposure time after presetting the aperturestop in preference.

As a through-the-lens type of photometric system to be used in a singlelens reflex camera, both a reduced aperture photometric system and amaximum-aperture photometric system have been employed.

Since the reduced-aperture photometric system in a single lens reflexcamera carries out the photometry after the aperture of an objective hasbeen reduced, it has disadvantages that the field of a view finderbecomes dark and results in inconvenience upon operation such as focusadjustment and the like, and that because the intensity of the incidentlight to the photoelectric element is weakened by the reduced apertureof the diaphragm blades, the effect of the light coming through the viewfinder eye-piece appears distinctly and results in errors at themeasured value of photometry.

Because of the aforementioned disadvantages, in a through-the-lens typeof single lens reflex cameras, the maximum-aperture photometric systemhas been more frequently employed.

However, the maximum-aperture photometric system has a disadvantage thatbecause a difference would normally occur between the preset aperturestop value and the aperture stop value to which the aperture is actuallyreduced upon exposure of the film, not always a proper exposure can beattained, if the photometry is carried out after the aperture stop valuehas been preset and a photograph is taken on the basis of the measuredvalue of photometry.

It is due to the fact that when the photometry is carried out under themaximum-aperture state, the exposure time is preset, and the releasebutton is depressed, at first the aperture is reduced towards the presetaperture stop value, and then the actually reduced aperture may possiblynot become the aperture corresponding to said preset aperture stop valuedue to looseness or the like of the aperture stop mechanism, because theaperture stop blades are quickly moved to the reducedaperture positionsowing to a resilient force of a spring.

Especially, in case that a wide angle objective is used and a photographis taken at a small aperture of diaphragm blades, said difference growseven to 6 stop of the aperture, and thus it cannot be neglected.

According to the present invention, the above-mentioned disadvantageinthe maximum-aperture photometric system can be eliminated.

The present invention will be described with reference to theaccompanying drawings, wherein:

FIG. 1 is a block diagram showing the system according to the presentinvention,

FIG. 2 is a circuit diagram of an electric control section in onepreferred embodiment of the present invention, and

FIG. 3 is a diagram showing the changes in the output of thephoto-electric element employed in said embodiment;

FIG. 4 is an exploded perspective view of one preferred embodiment ofthe present invention.

The system according to the present invention is a system which carriesout an automatic exposure control through the various steps asillustrated in FIG. 1. In this figure, an arrow t, the direction fromleft to right indicates the transient of time.

The camera employing the system according to the present invention isprovided with an objective having an automatic aperture controlmachanism. Accordingly, even if the aperture stop has been preset at adesired aperture stop value, the diaphragm blades are still opened atthe maximum aperture, so that it is possible to carry out a focusadjustment and the like through a bright view finder.

After the preliminary operations for taking a photograph such as, forexample, an aperture stop preset, a focus adjustment, etc. have beencarried out, at first the release button is depressed as shown in FIG.1.

If the release button is depressed, in the next stage the aperture isreduced towards the predetermined aperture stop value, andsimultaneously therewith a quick return mirror jumps up. As a mechanismfor such purpose, any known mechanism may be employed.

Then, a photometry by means of a photoelectric element is conducted. Thephotoelectric element is disposed behind the objective within thecamera. Therefore, the light projected onto the photoelectric cell isonly the light which has passed through the aperture of the stop whichwas actually reduced. Then the first blind of a focal plane shutter isreleased to start exposure of the film.

In this connection, upon exposure of the film, the photoelectric elementis adapted to be retracted out of the optical path for taking aphotograph. As means for carrying out this operation, various meansknown in the prior art can be employed such as, for instance, means formounting the photoelectric element on the preceding curtain of theshutter, or means for mounting the photo-electric element in front ofthe film surface so as to be freely erected up or laid down.

Since the time available for the photometry is an extremely short timeinterval (normally several tens milliseconds) after the step of jumpingup of the quick return mirror and reducing the aperture until the stepof releasing the first blind, as the photoelectric element, one having aquick photoelectric response is required. A silicon photovoltaic cell, aselenium photovoltaic cell, etc. are photoelectric elements which aresuitable for this purpose.

Then a timing device for controlling the exposure time is actuated. Andfinally a second blind of the focal plane shutter is released by thetiming device, whereby the shutter is closed and the exposure iscompleted.

Subsequently to the completion of exposure, the diaphragm blades, thequick return mirror, the timing device, etc. are restored to theirinitial states prior to the exposure, as is the case with the knowncameras in the prior art.

FIG. 2 is a circuit diagram of an electric control section of onepreferred embodiment of the present invention.

In this figure, reference character P represents a photoelectricelement. The photoelectric element P is mounted on the first blind ofthe focal plane shutter. Alternatively, the photoelectric element P maybe disposed in front of the film surface, for instance, just before theshutter blinds so as to be freely erected up or laid down, as describedpreviously, in such-manner that it may be kept in an erected state untilthe step of photometry illustrated in FIG. 1 and then it may be laiddown to be retracted out of the optical path for taking a photographjust prior to the release of the preceding curtain of the shutter.Reference characters T,, T T, and T represent transistors, respectively,while reference FT represents a field-effect transistor. Referencecharacter C, represents a capacitor, which is connected between the gateof the field-efiect transistor FT and the emitter of the transistor 1",.Reference character R, represents a resistor that is connected acrossthe capacitor C, via a switch 8,. Reference character C, represents acapacitor forming a part of a timing circuitry, which is connected atone end to the collector of the transistor T and at the other end to apositive terminal of a power supply battery E. Reference characters R RR and R represent resistors, respectively, and reference character Mrepresents an electromagnet which causes the second blind of the focalplane shutter to be released upon its actuation. Reference characters S,and S represent normally closed switches, which are linked with thefirst blind of the focal plane shutter so that they may be opened uponrelease of said .first blind. Reference character 8,, represents anormally opened switch, which is linked with the shutter release buttonso as to be closed upon its depression.

Now the operation of the circuit will be explained. By depressing theshutter release button, at first the switch S is closed. By the closureof the switch 8,, the transistor T becomes conducting to cause theelectromagnet M to be energized, and thereby the second blind of theshutter is locked at its starting position.

Then, the aperture of the objective is reduced, and simultaneouslytherewith the quick return mirror jumps up.

By the jump up of the quick return mirror, the photoelectric elementbecomes irradiated with the incident light. The intensity of the lightprojecting onto the photoelectric element P is that corresponding to thegiven combination of the brightness of the subject and the reduced sizeof the aperture.

The output current of the photoelectric element P changes as illustratedin FIG. 3. In more particular, after the quick return mirror has begunto rise at the point 0, the light projecting onto the photoelectricelement P becomes successively stronger as the mirror rises higher, andthereby the photoelectric current i, is increased. When the mirror hasreached the highest position, the current attains its maximum value iThereafter, when the first blind of the shutter has been released, thephotoelectric element P mounted on said first blind of the shutterbegins to be retraced out of the optical path for taking a photograph,and consequently the photoelectric current i, is reduced until itbecomes zero at the point B.

The output current of the photoelectric element P is proportional to theintensity of the incident light passed through the reduced aperture.Therefore, the output current varies according to the various aperturestop values and the degrees of brightness of the subject as illustratedat i, and i Through the base-collector circuit of the transistor T,flows a current which is proportional to the output current 2,, i i, orthe like of the photoelectric element P. Owing to the output of thetransistor T,, a voltage corresponding to the photoelectric current i,,i i or the like is generated across the resistor R,, and thus across thecapacitor C,. This voltage is a voltage corresponding to the givencombination of the area of the reduced aperture of the stop and thebrightness of the subject. Subsequently when the first blind of theshutter is released, the switches S, and S, are opened in a linkedmanner therewith. As the first blind of the shutter is moved, thephotoelectric element P is retracted out of the optical path, andaccordingly its output current is reduced to zero as illustrated in FIG.3. However, since the switch S, is opened and the input impedance of thefield-effect transistor FT is extremely high, the voltage across thecapacitor C, does not decay, even though the output current of thephotoelectric element P has been reduced to zero and thus the outputcurrent of the transistor T, has been reduced to zero. In other words,the output current of the photoelectric element P, that is, theintensity of the incident light onto the photoelectric element P isstored in the capacitor C, in the form of voltage.

On the other hand, from the moment when the switch S, has been opened,charging of the capacitor C is commenced, and since the output currentof the field-effect transistor FT is a current proportional to thevoltage across the capacitor C,, the charging current for the capacitorC, which is a current amplified by the transistor T, from said outputcurrent, is proportional to the voltage across the capacitor C,. Whenthe voltage across the capacitor C, has reached the trigger level forswitching the transistor T said transistor T becomes conducting, whilethe transistor T becomes non-conducting and the electromagnet M isdenergized, resulting in unlocking of the second flind of the shutter,so that the shutter is closed and thus the exposure is completed.

Because the time interval from the point of time when the switch S isopened (the point of time when the first blind of the shutter isreleased) until the point of time when the voltage across the capacitorC, reaches the trigger level and thereby the second blind of the shutteris released corresponds to the voltage across the capacitor C,, as willbe obvious from the preceding description, the exposure time correspondsto the actually reduced aperture of the stop and the brightness of thesubject, and in this way the automatic exposure control is achieved. Afixed diaphragm ring 2 and a movable diaphragm ring 5 located behind anobjective 1 have, as shown in the drawing, diaphragm blade driving pins3a and 3b to actuate the diaphragm blade 4, respectively.

The movable diaphragm ring 5 has an arm 5a, the leading end 512 of whichis adapted to contact with a connecting lever 8 against the action ofspring 9 biased in the direction to reduce the opening of the aperturewhen an objective assembly is mounted on the camera body.

Therefore, after the objective assembly has been mounted on the camerabody, the diaphragm is always kept open and the field of the view-finderis kept bright.

When taking a photograph, a preset ring 6 is rotated clockwisebeforehand according to the brightness of the object to be photographedand a stopper 7 is engaged with indented portion 6b at a position inaccordance with the aperture stop value thereby setting the diaphragm.

After focusing has been made with the diaphragm opened at its maximumaperture, a release button (not shown) is depressed. Then, a quickreturn mirror jumps up, and at the same time, the connecting lever 8 ismoved away from the end 5b of the arm 5a of the movable diaphragm ring 5so as to rotate the ring 5 clockwise by the tension of the spring 9biased in the direction to reduce the aperture opening and allow the arm5a to strike against the protruding part 6a ,of the preset ring 6,thereby the aperture is reduced to the preset stop value. 1

When member 19 has received the information that the aperture openinghas been reduced to the preset stop value, it strikes a bent portion 16bat the lower end of a mirror actuating lever 16 thereby to rotate thelever 16 counterclockwise about the center of rotation 16d. The mirroractuating lever 16 has a connecting dented part l6e, a connecting hole16c and a protruding part 160 and is always biased at its upper leftside end 16f in the direction to return the quick return mirror 10 intoits original position by the action of a spring 30. The connectingdented part 16e is connected with a pin 17d of Mirror actuating lever 17and the connecting hole 160 is connected with an upper end 17a of themirror actuating lever 17 through a spring 31, so that the lever 17 maymove in conjunction with the movement of lever 16. When the mirroractuating lever 17 is rotated counterclockwise around the center ofrotation, 17b in pursuit of the mirror actuating lever 16, a mirrorframe supporting member 18 is moved upwardly about the center ofrotation 18b by means of pin 170 of the lever 17 which can slide along agroove 18a of the mirror frame supporting metal 18. The quick returnmirror 10 is fixedly secured to frame supporting member 18, so that themirror 10 can also move upwardly. By the upward movement of the mirror10, aphotoelectric element 11 having a fast photoelectric responsebecomes irradiated with the incident light and photometry is made.Thereafter, the protruding part 16a of the mirror actuating lever 16strikes against a hook 20 of a connecting lever 21 biased by the actionof a spring 29.

The connecting lever 21 is linked with a connecting lever 22 by means ofa pin 21a and the connecting lever 22 is linked with a light receiverretracting lever 23 by means of a pin 22a, so that when the hook 20 isdisengaged from the connecting lever 21 the light receiver retractinglever 23 is rotated clockwise around the center of rotation 23c and theleft end 23a of the lever 23 moves over and away from the engaging part12a of the light receiver 12 which is biased by the action of a spring32 to retract the light receiver 12 out of the optical path. On theother hand, simultaneously with the completion of retraction of thelight receiver 12 out of the optical path, the right end 23b of thelight receiver retracting lever 23 strikes against and disengages a hook24. Hook 24 engages gear 25 of drum 13a for the first blind of theshutter, so that the first blind 13 starts its operation and the lightpasses through an aperture thereby commencing the exposure of the film.

Then, a timing device for controlling the exposure time (shown in FIG.2) is actuated. After a lapse of time determined by the timing device, ahook 33 is disengaged from a speed control gear 28 of drum 14a for thesecond blind of the shutter. As a result, the second blind 14 is closedto complete the exposure of the film, and the quick return mirror 10 andthe light receiver 12 are returned to their original positions based onthe information generated from the second blind of the shutter.

Alternatively, it is also possible to mount the photoelectric element onthe first blind of the shutter. The location of the photoelectricelement is not essential to the present invention.

As described, according to the present invention, since provision ismade such that after the depression of the shutter release button of acamera, the aperture is reduced from its full-opened state to the presetaperture stop value and simultaneously therewith the quick return mirroris caused to jump up, then photometry is carried out with respect to thelight passed through the reduced aperture of the stop, and the automaticexposure control is carried out on the basis of the value obtained bythe photometry; it is enabled to conduct preliminary operations fortaking a photograph such as focus adjustment while looking at a brightview finder field, and also the preset invention serves to entirelyeliminate the error of the actually reduced aperture of the stop withrespect to the preset aperture stop value, which was inevitableaccording to the maximum-aperture photometric system in the prior art.

What is claimed is:

1. An automatic exposure control system for a single lens reflex cameraof the type having a shutter release, an adjustable aperture, and aquick return mirror comprising:

means for reducing the size of the aperture from its maximum openedstate to a selected smaller size, said aperture reducing means beingactivated by the shutter release,

means for causing the quick return mirror to move from a first positionin the light path to a second position which does not intercept thelight path simultaneously with the reduction of the aperture,

a light responsive signal generating element normally situated out ofthe light path, said element being positioned to intercept the lightpath and generate a signal responsive to the light detected after saidquick return mirror has moved, and means for moving said element afterits exposure to the light path to a location which does not interceptthe light path, and

automatic means for controlling exposure time responsive to said signal.

2. The control system according to claim 1 wherein the light responsivesignal generating element is a photo-voltaic element having a fastphotoelectric response.

3. The control system according to claim 1 wherein the light responsivesignal generating element is disposed behind the quick return mirror.

4. The control system according to claim 1 further comprising anelectric shutter whose open time is controlled by said means forcontrolling exposure time.

5. A method for controlling exposure automatically for a single lensreflex camera of the type having a shutter release, an adjustableaperture, a shutter, a quick return mirror and a light responsive signalgenerating element comprising:

reducing the size of the aperture from its maximumopened state to apreset lesser size when the shutter release button is depressed,activating the quick return mirror to move from its normal position inthe light path to a second position which does not intercept the lightpath simultaneously with the aperture reduction, causing the lightresponsive signal generating element to intercept the light path afteractivation of the mirror and to generate a signal responsive to thelight detected,

then moving the light responsive signal generating element out of thelight path and controlling exposure time in response to said signal.

' ment will intercept the light path when the mirror is 6. The methodaccording to claim 5 wherein the light responsive signal generatingelement is a photovotaic element having a fast photoelectric response.

7. The method according to claim 8 wherein said shutter is an electricshutter. I

8. The method according to claim 5 wherein the step of causing the lightresponsive signal generating element to intercept the light pathcomprises the step of moving the light responsive signal generatingelement to a position in which it intercepts the light path.

9. The method according to claim 5 wherein the step of causing the lightresponsive signal generating element to intercept the light pathcomprises the step of positioning the light responsive signal generatingelement behind the quick return mirror so that the elemoved to itssecond position.

1. An automatic exposure control system for a single lens reflex cameraof the type having a shutter release, an adjustable aperture, and aquick return mirror comprising: means for reducing the size of theaperture from its maximum opened state to a selected smaller size, saidaperture reducing means being activated by the shutter release, meansfor causing the quick return mirror to move from a first position in thelight path to a second position which does not intercept the light pathsimultaneously with the reduction of the aperture, a light responsivesignal generating element normally situated out of the light path, saidelement being positioned to intercept the light path and generate asignal responsive to the light detected after said quick return mirrorhas moved, and means for moving said element after its exposure to thelight path to a location which does not intercept the light path, andautomatic means for controlling exposure time responsive to said signal.2. The control system according to claim 1 wherein the light responsivesignal generating element is a photo-voltaic element having a fastphotoelectric response.
 3. The control system according to claim 1wherein the light responsive signal generating element is disposedbehind the quick return mirror.
 4. The control system according to claim1 further comprising an electric shutter whose open time is controlledby said means for controlling exposure time.
 5. A method for controllingexposure automatically for a single lens reflex camera of the typehaving a shutter release, an adjustable aperture, a shutter, a quickreturn mirror and a light responsive signal generating elementcomprising: reducing the size of the aperture from its maximum-openedstate to a preset lesser size when the shutter release button isdepressed, activating the quick return mirror to move from its normalposition in the light path to a second position which does not interceptthe light path simultaneously with the aperture reduction, causing thelight responsive signal generating element to intercept the light pathafter activation of the mirror and to generate a signal responsive tothe light detected, then moving the light responsive signal generatingelement out of the light path and controlling exposure time in responseto said signal.
 6. The method according to claim 5 wherein the lightresponsive signal generating element is a photovotaic element having afast photoelectric response.
 7. The method according to claim 8 whereinsaid shutter is an electric shutter.
 8. The method according to claim 5wherein the step of causing the light responsive signal generatingelement to intercept the light path comprises the step of moving thelight responsive signal generating element to a position in which itintercepts the light path.
 9. The method according to claim 5 whereinthe step of causing the light responsive signal generating element tointercept the light path comprises the step of positioning the lightresponsive signal generating element behind the quick return mirror sothat the element will intercept the light path when the mirror is movedto its second position.